From 2cd96aa5bbcf5a13381acf9b22ef08ca090deff6 Mon Sep 17 00:00:00 2001
From: Shawn Hoffman <godisgovernment@gmail.com>
Date: Sun, 30 Sep 2018 17:58:37 -0700
Subject: [PATCH] mx sram: fix checksum calc; use Common::BigEndianValue for
 rtc field.

---
 Source/Core/Core/HW/EXI/EXI_DeviceIPL.cpp |  5 ++---
 Source/Core/Core/HW/Sram.cpp              | 10 ++++++----
 Source/Core/Core/HW/Sram.h                |  7 ++++---
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/Source/Core/Core/HW/EXI/EXI_DeviceIPL.cpp b/Source/Core/Core/HW/EXI/EXI_DeviceIPL.cpp
index cb827f5c7c..99c6e0cac4 100644
--- a/Source/Core/Core/HW/EXI/EXI_DeviceIPL.cpp
+++ b/Source/Core/Core/HW/EXI/EXI_DeviceIPL.cpp
@@ -127,7 +127,7 @@ CEXIIPL::CEXIIPL()
   }
 
   // Clear RTC
-  memset(g_SRAM.rtc, 0, sizeof(g_SRAM.rtc));
+  g_SRAM.rtc = 0;
 
   // We Overwrite language selection here since it's possible on the GC to change the language as
   // you please
@@ -250,8 +250,7 @@ void CEXIIPL::SetCS(int cs)
 
 void CEXIIPL::UpdateRTC()
 {
-  const u32 rtc = Common::swap32(GetEmulatedTime(GC_EPOCH));
-  std::memcpy(g_SRAM.rtc, &rtc, sizeof(u32));
+  g_SRAM.rtc = GetEmulatedTime(GC_EPOCH);
 }
 
 bool CEXIIPL::IsPresent() const
diff --git a/Source/Core/Core/HW/Sram.cpp b/Source/Core/Core/HW/Sram.cpp
index 155cafcfcd..cafc5e2f5c 100644
--- a/Source/Core/Core/HW/Sram.cpp
+++ b/Source/Core/Core/HW/Sram.cpp
@@ -78,14 +78,16 @@ void SetCardFlashID(const u8* buffer, u8 card_index)
 
 void FixSRAMChecksums()
 {
+  // 16bit big-endian additive checksum
   u16 checksum = 0;
   u16 checksum_inv = 0;
   for (auto p = reinterpret_cast<u16*>(&g_SRAM.settings.rtc_bias);
        p != reinterpret_cast<u16*>(&g_SRAM.settings_ex); p++)
   {
-    checksum += *p;
-    checksum_inv += ~*p;
+    u16 value = Common::FromBigEndian(*p);
+    checksum += value;
+    checksum_inv += ~value;
   }
-  g_SRAM.settings.checksum = Common::swap16(checksum);
-  g_SRAM.settings.checksum_inv = Common::swap16(checksum_inv);
+  g_SRAM.settings.checksum = checksum;
+  g_SRAM.settings.checksum_inv = checksum_inv;
 }
diff --git a/Source/Core/Core/HW/Sram.h b/Source/Core/Core/HW/Sram.h
index f088f8b614..ae2b156b4c 100644
--- a/Source/Core/Core/HW/Sram.h
+++ b/Source/Core/Core/HW/Sram.h
@@ -36,6 +36,7 @@ distribution.
 
 #include <array>
 #include "Common/CommonTypes.h"
+#include "Common/Swap.h"
 
 using CardFlashId = std::array<u8, 12>;
 
@@ -79,8 +80,8 @@ struct SramFlags
 struct SramSettings
 {
   // checksum covers [rtc_bias, flags]
-  u16 checksum;
-  u16 checksum_inv;
+  Common::BigEndianValue<u16> checksum;
+  Common::BigEndianValue<u16> checksum_inv;
 
   // Unknown attributes
   u32 ead0;
@@ -119,7 +120,7 @@ union Sram
   u8 raw[0x44];
   struct
   {
-    u8 rtc[4];
+    Common::BigEndianValue<u32> rtc;
     SramSettings settings;
     SramSettingsEx settings_ex;
   };